Do O2 sensors wear out? Or do they work or not? I'm curious if its similar to a dirty air filter where they slowly degrade and a new one makes a difference. I'm curious for my 91 LX but also for 97 Q45 where the O2 sensors are $95 X4!!
Yes, they wear out. Sometimes over many years, sometimes abruptly. They should last many, many thousands of miles, as long as the car isn't running like crap. I've seen originals go well over 100K without problems.
bosh specs state 93 down with o2 sensors last 60,000 miles and 94 and up will last 100,000 miles these are approximate but the check engine light should let you know when to change....usually the heated element shorts out but to test sensors a chilton manual will show you how to test an o2 sensor with a multimeter to ensure its bad
click on link heres a good article on o2 sensors and click on links within page under (These links will help you learn more theres some good info there.... http://auto.howstuffworks.com/question257.htm
Above info is very good. They do lose amplitude and frequency [in switching] over time, and if contamination or some other issue occurs, then they can crap out quite quickly, as Jess said.
FWIW, on the OBD-II car, the rear O2's are for monitoring of the catalyzation process. Unless there was a direct issue, I would not go out of my way to replace those rear two. The front two handle A/F trim.
Usually O2 sensors will set code 41/91 when you dump the codes. Here's the link to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great.
IF your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.
Codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.
Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.
For those who are intimidated by all the wires & connections, see http://www.actron.com/product_detail.php?pid=16153 for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Walmart.
Code 41 or 91 - O2 indicates system lean. Look for a vacuum leak or failing O2 sensor.
The computer sees a lean mixture signal coming from the O2 sensors and tries to compensate by adding more fuel. Many times the end result is an engine that runs pig rich and stinks of unburned fuel.
The following is a Quote from Charles O. Probst, Ford fuel Injection & Electronic Engine control:
"When the mixture is lean, the exhaust gas has oxygen, about the same amount as the ambient air. So the sensor will generate less than 400 Millivolts. Remember lean = less voltage.
When the mixture is rich, there's less oxygen in the exhaust than in the ambient air , so voltage is generated between the two sides of the tip. The voltage is greater than 600 millivolts. Remember rich = more voltage.
Here's a tip: the newer the sensor, the more the voltage changes, swinging from as low as 0.1 volt to as much as 0.9 volt. As an oxygen sensor ages, the voltage changes get smaller and slower - the voltage change lags behind the change in exhaust gas oxygen.
Because the oxygen sensor generates its own voltage, never apply voltage and never measure resistance of the sensor circuit. To measure voltage signals, use an analog voltmeter with a high input impedance, at least 10 megohms. Remember, a digital voltmeter will average a changing voltage." End Quote
Measuring the O2 sensor voltage at the computer will give you a good idea of how well they are working. You'll have to pull the passenger side kick panel off to gain access to the computer connector. Remove the plastic wiring cover to get to the back side of the wiring. Use a safety pin or paper clip to probe the connections from the rear. The computer pins are 29 (LH O2 with a dark green/pink wire) and 43 (RH O2 with a dark blue/pink wire). Use the ground next to the computer to ground the voltmeter.
Most of the common multimeters have a resistance scale. Be sure the O2 sensors are disconnected and measure the resistance from the O2 sensor body harness to the pins on the computer.
Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter. Do not attempt to measure the resistance of the O2 sensors, it may damage them.
The O2 sensor ground (orange wire with a ring terminal on it) is in the wiring harness for the fuel injection wiring. I grounded mine to one of the intake manifold bolts
Oxygen sensors do deterioriate as they get older. If one goes bad pre-mature, well, maby it was a bad sensor from the factory, but if the problem of sensors going downhill too fast, it might be because something is killing them. Burning oil will do it, and so will race gas. Sometimes even burning rich all the time wil do it as the fuel residues will build up on the sensor. As they get older, they switch slower and don't read as accuratly. When the light comes on the dash on a OBDI car, that means it is really dead. If your sensors are old, change them, the money you save in gas will make it worth it.